1. Field of the Invention
This invention relates to a silicon carbide substrate usable for integrated circuits or IC packages and a method of producing the same, and more particularly to a silicon carbide substrate having an excellent electrical insulation property by closely adhering a eutectic oxide layer onto a silicon carbide plate body and a method of producing the same.
2. Description of the Prior Art
Lately, electronic components such as semiconductors and the like are strongly directed to miniaturization or large-sized integration with the advancement of electronics industrial technology. Thus, the heat release value in integrated circuits increases with the large-sized integration of the electronic component, so that the heat dissipation of the substrate for the integrated circuit becomes significant. In the electronics industry, there are known and practiced various kinds of the substrates. Particularly, alumina sintered body, glass and the like are used for applications requiring high reliability. However, these substrates usually used are low in the thermal conductivity and poor in the heat dissipation, so that they have difficulty in solving problems due to heat accumulation, which is a very serious obstacle to inhibiting the large-sized integration of the electronic component.
As a material of the substrate solving the above problems, there have hitherto been examined beryllia, porcelain enamel and the like. However, the beryllia has a drawback that the production and handling are difficult owing to its toxicity. While, the porcelain enamel has drawbacks that the thermal expansion coefficient is large because a metallic plate is used as a substrate, and that frits are apt to take a dogbone structure, and that not only the cutting after the printing is difficult but also the laser trimming cannot be performed because cracks occur in the porcelain enamel at the cutting surface.
In any case, the conventionally known substrates have various drawbacks as previously mentioned.
The inventors have made various studies with respect to the provision of substrates capable of solving the above mentioned drawbacks, namely, substrates having a high thermal conductivity and very excellent properties usable for large-sized integrated circuit or IC package and found that the silicon carbide sintered body has high thermal conductivity, high thermal shock resistance, and high strength at both room temperature and elevated temperatures as compared with the conventional alumina sintered body (hereinafter referred to as alumina substrate) widely used as a substrate, and that the alumina substrate is largely different from a silicon chip usually used for the integrated circuit in the thermal expansion coefficient so that it is difficult to directly adhere the silicon chip to the alumina substrate, while the silicon carbide sintered body has a thermal expansion coefficient substantially equal to that of the silicon chip so that it can directly be adhered with the silicon chip. However, the silicon carbide sintered body has semiconductive properties but has no electrical insulation property, so that it is not yet used as a substrate up to now.
With the foregoing in mind, the inventors have made studies with respect to a method of imparting the electrical insulation property to the silicon carbide plate body in order to apply this plate body as a substrate to large-sized integrated circuits or IC packages.
In order to impart the electrical insulation property to the silicon carbide plate body, the inventors have attempted a method wherein an electrically insulating material such as vitreous substance composed of oxide or the like is applied and fused to the surface of the silicon carbide plate body to form an electrically insulating film, and a method wherein the silicon carbide plate body is oxidized to produce an electrically insulating film of silicon dioxide on the surface of the plate body. In the former method, however, the wettability and adherence between the silicon carbide plate body and the vitreous substance are poor, so that the film is apt to peel off from the plate body. Furthermore, defects of pinholes, cracking and the like are apt to be produced, so that the reliability is very low. On the other hand, according to the latter method, it is difficult to uniformly oxidize the surface of the silicon carbide plate body and the thickness of the resulting oxide film is apt to become nonuniform. Furthermore, the resulting silicon dioxide mainly produces cristobalite crystal, so that it is difficult to provide a uniform and dense film having a stable electrical insulation property.
In this connection, the inventors have made further studies with respect to the method for the formation of films solving the aforementioned drawbacks and having a stable electrical insulation property and found out that when the electrically insulating oxide film is formed on the surface of the silicon carbide plate body, SiO.sub.2 produced by surface oxidation of the siicon carbide plate body can form a eutectic oxide layer having a very good adherence and a high reliable electrical insulation property together with the oxide film, and as a result the invention has been accomplished.